Question 43894
 
  I guess these problems involve only the factorisation. i.e. We have to factorise the problems.
 
1)  {{{20x^4-12x^3-8x^2}}}
 =  {{{4x^2(5x^2-3x-2)}}}
 =  {{{4x^2(5x^2-5x+2x-2)}}}
 =  {{{4x^2(5x(x-1)+2(x-1))}}}
 =  {{{4x^2(x-1)(5x+2)}}}  Answer.
 
2)  {{{6x^2+2x-20}}}
 =  {{{6x^2+12x-10x-20}}}
 =  {{{6x(x+2)-10(x+2)}}}
 =  {{{(6x-10)(x+2)}}}
 =  {{{2(3x-5)(x+2)}}}  Answer
 
3)  {{{5w^2-20}}}
 =  {{{5(w^2-4)}}} = {{{5(w^2-2^2)}}}
 =  {{{5(w+2)(w-2)}}}  Answer.
 
4)  {{{5y^4-405}}}
 =  {{{5(y^4-81)}}} = {{{5(y^4-3^4)}}}
 =  {{{5(y^2+3^2)(y^2-3^2)}}}
 =  {{{5(y^2+3^2)(y+3)(y-3)}}}  Answer.

I hope it is now clear to you.

gsm